Your Question:

Hello

I do not understand the following in a database book:

Key1 = {State, Reg#}

Key2 = {SerialNo}

Step By Step Answers with Explanation

1. Key1 = {State, Reg#} and Key2 = {SerialNo} are both superkeys but not keys:

In the context of database design, a superkey is a set of attributes that can uniquely identify a tuple (row) in a relation (table). On the other hand, a key is a minimal superkey, which means it's a superkey that cannot be further reduced without losing its uniqueness property.

In the CAR relation, the combination of attributes {SerialNo, Make} is indeed a superkey. This means that using both "SerialNo" and "Make" together can uniquely identify a car. However, it is not a key because it's not minimal.

Here's why it's not minimal: